The present invention relates to the control of transmission power on communication channels in a radiocommunication system. More particularly, it relates to power control for certain communication channels useful for implementing high-speed data transmissions.
Power control procedures are known for radiocommunication systems, such as the GSM system (“Global System for Mobile communications”) or the UMTS system (“Universal Mobile Telecommunication System”). Their purpose is to improve performance for the reception of transmitted information, while limiting the risks of interference.
Power control is particularly sensitive when applied to data transmission channels which allow a high throughput, since a power that is too weak on such channels may cause a high error rate in the transmission, which is detrimental to the throughput offered. This is equally the case with control channels associated with a high-speed data transmission channel, since a power that is too weak on such channels may cause poor monitoring of the associated data transmission channel and therefore loss of useful information.
UMTS offers a high-speed data transmission functionality, referred to as HSDPA (“High Speed Downlink Packet Access”). An overview of this functionality may be found in the technical specification entitled 3GPP TS 25.308, Release 5, version 5.4.0, published in December 2003 by the 3GPP (“3rd Generation Partnership Project”).
HSDPA provides for the use of shared downlink transport channels, referred to as HS-DSCH (“High Speed-Downlink Shared CHannel”), multiplexed on physical channels HS-PDSCH (“High Speed-Physical Downlink Shared CHannel”), which enable a base station to transmit to high-speed data terminals. The terminals forward counter-response information to the base station, particularly acknowledgements and indications linked to the quality of the downlink transmissions, on dedicated uplink channels, referred to as HS-DPCCH (“High Speed-Dedicated Physical Control CHannel”).
For an HS-DSCH channel, one or more specific shared physical control channels, referred to as HS-SCCH (“High Speed-Shared Control CHannel”) must be provided. The signaling information carried by the HS-SCCHs identify the destination terminals for the blocks transmitted on the HS-DSCHs, and provide them with a certain number of indications which are useful for the reception of these blocks.
A base station implementing high-speed data transmission according to the HSDPA functionality distributes a power between the HS-PDSCH and HS-SCCH channels. The power to be distributed among the HSDPA downlink channels is typically the power remaining when a transmission power has been allocated to all of the dedicated and shared downlink channels.
Technical specification TS 25.214, version 5.7.0, Release 5, “Universal Mobile Telecommunications System (UMTS); Physical layer procedures (FDD)”, published in December 2003 by the 3GPP, specifies that the transmission power on the HS-SCCH can be defined by applying a margin in relation to the transmission power on a dedicated channel known as DPCCH (“Dedicated Physical Control CHannel”). However, this margin is defined in an optional manner, and so it must also be possible to control the power of the HS-SCCH channel in a different manner.
As far as the HS-PDSCH channels are concerned, nothing is specified to control their transmission power.
One object of the present invention is to avoid loss of information and a limitation of performance relative to certain communication channels, such as the HS-PDSCH and HS-SCCH channels.
Another object of the invention is to control the transmission power on certain shared communication channels, such as the HS-PDSCH and HS-SCCH channels, in an effective and appropriate manner.